The Huskers trail, 20-3.
Staring at a 17-point deficit, Nebraska needs a big play. On offense, there might be no better player in America (more 20-plus yard runs than both LaMichael James and Denard Robinson) to provide that than Martinez.
The best guess here is that Pelini wants more consistency in the passing game, including looks for receiver Niles Paul, who got a deep ball from Lee on his first drive. In that case, the senior is the best option.
Against a Texas secondary full of experienced, NFL-caliber talent, that's not a great idea, either.
Granted, the best option is just to not fall behind 17 points to a defense like Texas', but Nebraska has already expended that luxury. Whether it comes from Martinez, Lee, Paul or the defense, Nebraska has to make something happen fast, or it will suffer yet another painful loss to the Longhorns.